1. Field of the Invention
The invention relates to a vascular ablation apparatus and method. More particularly, the invention relates to a vascular ablation apparatus that delivers a sclerosing solution during the disruption and/or irritation of a vessel wall. The invention further relates to a vascular ablation method wherein disruption and/or irritation of the vessel wall is combined with the application of sclerosant.
2. Description of the Prior Art
Venous stasis is a common condition in which the flow of blood from the legs to the heart is abnormal. Most people assume that the heart pumps blood out to the legs and then pumps it back. That's only half right. Actually, the heart only pumps the blood out. Leg muscles pump it back. Every time a leg muscle tightens (called contraction), it squeezes the leg veins flat. Blood is pushed through the veins like toothpaste being squeezed from a tube. When everything is working normally, a series of one-way gates (called valves) make sure the blood can only move one direction; that is, toward the heart. However, when the valves are damaged, the “muscle pump” doesn't work (imagine a busy intersection with no traffic signals). This condition is called reflux and most often involves a large leg vein called the saphenous vein. When saphenous reflux is present, blood simply pools in the legs, causing everything from unsightly varicose veins to severe pain and ulceration of the skin.
The treatment options for venous stasis are currently limited. The traditional therapy used to treat venous reflux in the saphenous vein is surgical stripping and ligation. This procedure is performed by surgeons and often involves general anesthesia in a hospital setting. Vein stripping and ligation begins with an incision in the groin region to expose the saphenous vein; once identified the surgeon “ligates” or ties off the saphenous vein and small veins with sutures. A second incision is made either just below the knee or at the ankle for the same purpose. Once both ends of the vein are free, a thin wire-like instrument called the stripping tool is threaded through the vein from the groin to the second incision. The stripping tool is tied to the vein and the vein is pulled out, or stripped, and removed from the leg. Some common side effects from vein stripping and ligation surgery may include temporary pain or discomfort, bruising, hematoma, numbness, and less frequently wound infection.
In addition to stripping, laser treatment is currently available. Endovenous laser treatment allows delivery of laser energy directly into the blood vessel lumen in order to produce endothelial and vein wall damage with subsequent fibrosis. It is presumed that destruction of the greater saphenous vein with a laser is a function of thermal destruction. The presumed target is intravascular red blood cell absorption of laser energy. However, thermal damage with resorbtion of the greater saphenous vein has also been seen in veins emptied of blood. Therefore, direct thermal effects on the vein wall probably occur. The extent of tissue thermal injury is strongly dependent on the amount and duration of heat exposure.
Radio-Frequency treatments are also used. For example, The VNUS Closure procedure (www.vnus.com) is a minimally invasive option for patients with superficial venous reflux and varicose veins. Using radiofrequency (RF) energy and a catheter based approach, the closure procedure occludes veins thereby eliminating reflux.
Potential complications of laser and RF include, but are not limited to the following: vessel perforation, thrombosis, pulmonary embolism, phlebitis, hematoma, infection, paresthesia and skin burn. Treatment of veins located very close to the skin surface may result in a skin burn. Paresthesia may occur from thermal damage to adjacent sensory nerves. The risk of paresthesia is higher with treatment at or below the calf.
Vein sclerotherapy has been a treatment in Europe since the 1960's. It is an injection technique for treating various vein conditions such as; varicose veins, reticular veins, spider veins of the leg, and also some fine facial veins. Varicose and spider veins are predominant in women and affect about 40% of the population.
Sclerotherapy is the treatment of choice for the smaller spider or thread veins, which are so common on the face and legs. Sclerotherapy is a 30-minute, virtually painless procedure with huge advantages over surgery, including no general anesthetics, no stitches, no hospitalization and no time off work.
The mechanism of sclerotherapy is as follows. Vascular fibrosis and obliteration only occurs in response to irreversible endothelial cellular destruction and exposure of the underlying subendothelial cell layer. If an injected sclerosant is too weak, there may be no endothelial injury at all. If the sclerosant is a little stronger, the varicose vessel is damaged, but recanalization occurs and an incompetent pathway for retrograde blood flow persists. If the injected sclerosant is too strong, the varicose vessel endothelium is destroyed, but the sclerosant may flow into adjacent normal vessels and causes damage there as well. The key goal is to deliver a minimum volume and concentration of sclerosant that will cause irreversible damage to the endothelium of the abnormal vessel to be sclerosed, while leaving adjacent normal vessels untouched. It is important to protect normal superficial vessels, and it is critically important to avoid injuring the endothelium of deep veins, because deep vein thrombosis places patients at risk of death from thromboembolism, as well as causing permanent disability from chronic deep venous valvular insufficiency. The rational treatment of varicosities and telangiectasias by chemical sclerosis depends upon the ability to produce vascular endothelial damage that is irreversible in the area under treatment, but that does not extend to adjacent normal vessels.
Sclerosant is diluted with blood as it diffuses away from the site of injection. Thus, if a strong sclerosant is injected, there will be three zones of action. In zone 1, vascular endothelium is irreversibly injured; the vessel will be fully sclerosed and eventually will be completely replaced by a fibrous tissue. In zone 2, vascular endothelium is injured, and the vessel will be partially or completely thrombosed but will eventually recanalize. In zone 3, the sclerosant will be diluted below its injurious concentration, and there will be no endothelial injury.
Because dilution of the sclerosant with blood occurs immediately upon injection, the original injected concentration is of no real importance. What is important is the diluted concentration of sclerosant at the surface of the endothelium. An injected concentration that is perfectly effective in a spider vein (where sclerosant displaces blood rather than mixing with it) may be ineffective in a reticular feeding vein or a truncal varix simply because dilution reduces the final concentration so low that there will be no endothelial injury whatsoever. If the injected concentration is too high, dilution will leave the final concentration so high that endothelial damage will occur where it is not wanted. If the injected concentration is just right, dilution will leave a final concentration that is sufficient to injure the local varicose endothelium, but not high enough to damage normal superficial or deep veins. With big vessels, sclerotherapy alone is not sufficient to guarantee venous occlusion and destruction; success rate of sclerotherapy alone in permanently occluding the vein is about 60%, therefore enhancement of the sclerosis procedure is needed.
When one selects a particular volume and concentration of a chemical agent with which to sclerose a vessel, they explicitly or implicitly adjust the injected concentration and volume to take into account the dilution that will occur when the sclerosant is mixed with blood immediately after injection. One must also take into account the further dilution that will occur as the sclerosant flows or diffuses away from the site of injection.
Vascular spasm is usually and unwanted phenomena of vessels in general and veins in particular. Spasm of the greater saphenous vein can occur during a cardiac bypass surgery and after graft implantation. Arterial spasm can also occur and can result in an infarction. Vascular spasm also occurs with excessive manipulation of vessels with catheters or guide wires. Without any additional irritation venous spasm usually resolves spontaneously. Because of the cylindrical geometry of blood vessels, the volume contained in a vessel depends on the square of the vessel radius: the volume of any cylinder is calculated as (pi)(r2)(L) (where r is the radius and L is the length of the vessel). During spasm the diameter of the vessel is reduced dramatically, up to 5 to 10 fold smaller, decreasing the volume of blood within the vein by a magnitude of 25 to 100.
In view of the shortcomings of prior treatment techniques and apparatuses, a need exists for an improved apparatus and method for treating venous stasis. The present invention provides such an apparatus and method.